Merge branch 'fix-bpf_get_stack-with-PEBS'

Song Liu says:

====================
Calling get_perf_callchain() on perf_events from PEBS entries may cause
unwinder errors. To fix this issue, perf subsystem fetches callchain early,
and marks perf_events are marked with __PERF_SAMPLE_CALLCHAIN_EARLY.
Similar issue exists when BPF program calls get_perf_callchain() via
helper functions. For more information about this issue, please refer to
discussions in [1].

This set fixes this issue with helper proto bpf_get_stackid_pe and
bpf_get_stack_pe.

[1] https://lore.kernel.org/lkml/ED7B9430-6489-4260-B3C5-9CFA2E3AA87A@fb.com/

Changes v4 => v5:
1. Return -EPROTO instead of -EINVAL on PERF_EVENT_IOC_SET_BPF errors.
   (Alexei)
2. Let libbpf print a hint message when PERF_EVENT_IOC_SET_BPF returns
   -EPROTO. (Alexei)

Changes v3 => v4:
1. Fix error check logic in bpf_get_stackid_pe and bpf_get_stack_pe.
   (Alexei)
2. Do not allow attaching BPF programs with bpf_get_stack|stackid to
   perf_event with precise_ip > 0, but not proper callchain. (Alexei)
3. Add selftest get_stackid_cannot_attach.

Changes v2 => v3:
1. Fix handling of stackmap skip field. (Andrii)
2. Simplify the code in a few places. (Andrii)

Changes v1 => v2:
1. Simplify the design and avoid introducing new helper function. (Andrii)
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>